Device for forming annular articles from powder material

ABSTRACT

The present invention relates to a device for forming tubular articles from powder material including an upper pressing punch, a lower punch, a core pin and a matrix having an inner periphery corresponding to the outer periphery of the upper and lower punch, a molding cavity being defined between the upper and lower punch, the core pin and the matrix, whereby the core pin is movable in relation to the matrix. According to the invention the upper pressing punch is arranged to actuate movement of the core pin or the matrix during compacting of a powder in the molding cavity so that the pressing punch and the core pin or the matrix move together.

FILED OF THE INVENTION

[0001] The present invention relates to a device for forming tubulararticles from powder material. More particularly, the present inventionis directed to a device comprising an upper pressing punch, a lowerpunch, a core pin and a matrix having an inner periphery correspondingto the outer periphery of the upper and lower punch, a molding cavitybeing defined between the upper and lower punch, the core pin and thematrix, whereby the core pin is movable in relation to the matrix.

BACKGROUND OF THE INVENTION

[0002] A problem encountered when making tubular articles, such asbearing rings, by compacting powdered metal located in a mold cavityhaving a stationary bottom wall and stationary side walls is unevencompacting of the articles, especially if the height of the tubulararticle is large in comparison with the wall thickness. This is due tofriction between the particles in the metal powder and the walls of themolding cavity during the compacting step so that a large part of thecompacting energy is consumed as frictional heat, the result being thatthe compacted tubular article is more compacted in the parts lyingnearest the pressing punch than in other parts.

[0003] EP-A1-0 450 784 discloses a device for forming cylindricalcompacts. In this device all the components except the lower punch ismoved with different travelling speeds during the compacting step, whichleads to a complicated and expensive construction of the device.

SUMMARY OF THE INVENTION

[0004] An object of the present invention is to provide a device inwhich the compacting of the tubular articles is more even than in adevice having a mold cavity with a stationary bottom wall and stationaryside walls, and which device is of a simple construction.

[0005] According to one aspect, the present invention provides a devicefor forming tubular articles from powder material comprising an upperpressing punch, a lower punch, a core pin and a matrix having an innerperiphery corresponding to an outer periphery of the upper and lowerpunch, a molding cavity being defined between the upper and lower punch,the core pin and the matrix, whereby the core pin is movable in relationto the matrix, wherein the upper pressing punch is arranged to actuatemovement of the core pin or the matrix during compacting of a powder inthe molding cavity so that the pressing punch and the core pin or thematrix move together.

[0006] In a preferred embodiment, the core pin is movable between afirst position in which the upper end thereof is located in line with,or above, the upper wall of the matrix, and a second position in whichthe upper wall of the core pin is located below the upper wall of thematrix. The core pin can advantageously be biased against the firstposition. Furthermore, the upper pressing punch has in a first positiona part of its lower wall in contact with the upper end wall of the corepin, so that the pressing punch will force the core pin to followdownwards movement thereof from its first position, and the upperpressing punch is preferably moveable upwards from its first position inorder to open up the molding cavity for insertion of powder materials.The lower punch can advantageously be upwardly moveable in order toeject a compacted article from the molding cavity.

[0007] In another embodiment the core pin is an integral part of theupper pressing punch.

[0008] It is pointed out that the term “tubular articles” includesarticles having various sectional shapes such as polygonal (e.g. -rectangular), circular, etc. The sectional shape can also be an opentubular shape (i.e. - with other shapes than circular), for example aU-shaped section.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The invention will now be further described with reference to theenclosed Figures, of which;

[0010]FIG. 1 is a schematic sectional view of a device according to apreferred embodiment of the invention, showing the device immediatelybefore the pressing step, and

[0011]FIG. 2 is a view similar to FIG. 1, showing the device in the endof the pressing step.

DESCRIPTION OF EMBODIMENTS

[0012] The device in FIGS. 1 and 2 comprises a cylindrical core pin 1and an annular matrix 2, which has an inner diameter that is larger thanthe diameter of the core pin 1 so that a cylindrical space is definedbetween the core pin and the matrix. A lower punch 3 having the form ofa hollow cylinder is dimensioned to fit into the annular space betweenthe core pin and the matrix and the upper wall of the lower punch 3constitutes the bottom wall of a molding cavity 4. A work piece 5 ofpowder metal is disposed in this cavity in FIG. 1.

[0013] A pressing punch 6 having a cylindrical body with a diametercorresponding to the inner diameter of the matrix 2 is slidable withinthe inner cylindrical space defined by the matrix. The lower end surface7 of the pressing punch has a central recess into which the upper endportion 8 of the core pin 1 is fitted.

[0014] According to the invention the core pin 1 is slidable within thelower punch 3 and is biased to a first position by a spring 9 disposedbetween the lower end surface of the core pin and an opening in thefoundation. In the first position of the core pin its upper end surfaceis flush with the upper surface of the matrix 2 in order to facilitateremoval of superfluous powder filled into the molding cavity. In FIG. 1,the core pin is disposed in its first position.

[0015] In FIG. 1 the pressing punch 6 is placed in a first position fromwhich the step of compacting the work piece 5 takes place by pressingthe punch 6 downwardly with a pressing force P. In the first position ofthe pressing punch, the surface of the central recess in its lower endsurface 7 abuts the surface of the upper end portion 8 of the core pinand the side wall of the upper end portion 8 abuts the vertical wall ofthe recess in the lower end surface 7 of the pressing punch. The corepin is thus forced to follow downward movement of the pressing punchfrom its first position.

[0016] During the pressing step the pressing punch and the core pin willthus move together. Thereby, the friction forces created between themoving wall of the core pin and the particles in the powder material 5disposed in the molding cavity 4 will have an opposite directionrelative to the frictional forces created between the particles in thepowder material and the stationary matrix wall. The friction forcescreated during the pressing step will thus balance each other and thepowder material will be more evenly compacted throughout the heightthereof.

[0017] In FIG. 2 the inventive device is shown in the end of thepressing step. The powder material in the molding cavity being compactedto an annular ring 10. The lower punch 3 is by some suitable meansarranged to act as a knock-out punch after the pressure P on thepressing punch 6 has been released, so as to eject the finished ring 10from the molding cavity. For example, hydraulic pistons disposed in thefoundation under the lower punch 3 can be arranged push the lower punch3 upwardly when actuated. Before the ring 10 is ejected the upperpressing punch 6 is moved upwards to a position above the position shownin FIG. 1 in order to facilitate removal of the ring 10 from the moldingcavity 4.

[0018] It is not unusual that the device is used also for compactingpowder material in the form of preshaped tubular articles or greenbodies. The devices should therefore preferably be designed tofacilitate insertion of such preformed articles into the molding cavity.

[0019] The described embodiment can of course be modified in severalrespects while remaining within the scope of the invention. For example,the pressing punch and the core pin can form an integral piece. However,such a structure makes the use of the device for preparatory or greencompacts complicated and is therefore not preferred. Moreover, thepressing punch can have a totally flat lower end surface instead of therecess disclosed in the described embodiment. However, this is notpreferred since the guiding of the core pin will then be decreased.Furthermore, the matrix can be arranged to move together with thepressing punch during the pressing step instead of the core pin, whichin such an embodiment is stationary. The scope of invention shouldtherefore be limited only of the wording of the enclosed patent claims.

[0020] While the present invention has been described by reference tothe above-mentioned embodiments, certain modifications and variationswill be evident to those of ordinary skill in the art. Therefore thepresent invention is to be limited only by the scope and spirit of theappended claims.

What is claimed is:
 1. A device for forming tubular articles from powdermaterial comprising an upper pressing punch, a lower punch, a core pinand a matrix having an inner periphery corresponding to an outerperiphery of the upper and lower punch, a molding cavity being definedbetween the upper and lower punch, the core pin and the matrix, wherebythe core pin is movable in relation to the matrix, wherein the upperpressing punch is arranged to actuate movement of the core pin or thematrix during compacting of a powder in the molding cavity so that thepressing punch and the core pin or the matrix move together.
 2. Thedevice according to claim 1, wherein the core pin is an integral part ofthe upper pressing punch.
 3. The device according to claim 1, whereinthe core pin is movable between a first position in which the upper endthereof is located in line with or above the upper wall of the matrixand a second position in which the upper wall of the core pin is locatedbelow the upper wall of the matrix.
 4. The device according to claim 3,wherein the core pin is biased against the first position.
 5. The deviceaccording to claim 3, wherein the upper pressing punch in the firstposition has a part of its lower wall in contact with the upper end wallof the core pin so that the pressing punch will force the core pin tofollow downwards movement thereof from its first position, and that theupper pressing punch is moveable upwards from its first position inorder to open the molding cavity (4) for insertion of powder material.6. The device according to claim 1, wherein the lower punch is upwardlymoveable in order to eject a compacted article from the molding cavity.